The invention relates to an apparatus for examining female breasts with at least one ultrasonic transducer for scanning level layer areas in a stationary scanning position, with which ultrasonic beams can be coupled into at least one breast over a coupling medium, and to a transporting unit for displacing the or each ultrasonic transducer between scanning positions by a pre-determined path length.
The invention furthermore relates to a method for reducing artifacts of an ultrasonic image at least of a female breast, for which an ultrasonic transducer, for scanning level layer areas in a stationary scanning position, is shifted over at least the one breast by a transporting unit by a fixed path length between scanning positions and by consecutively shifting and a three-dimensional ultrasonic image is recorded and stored in an assigned memory unit by consecutively shifting and assigning a data value, corresponding to the shifting, to a layer image of an image sequence.
Such an apparatus and such a method are already known from the article xe2x80x9cAcquisition and Stereoscopic Visualization of Three-Dimensional Ultrasonic Breast Dataxe2x80x9d by A. Hernandez, O. Basset, I. Dautraix et al., published in the journal IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, volume 43, Jul. 1996, pages 576 to 580. The article discloses an apparatus with an ultrasonic transducer, which is set up to record two-dimensional layer images and can be shifted by means of a transporting unit by a specified path length between scanning positions, in which the scanning of the two-dimensional image takes place. The disclosed apparatus furthermore comprises a memory unit for storing the layer images recorded by the ultrasonic transducer, a data value, corresponding to the shifting, being assigned. By means of this assigning, a three-dimensional ultrasonic image is produced by the disclosed recording method and stored in the memory unit. For the stereoscopic representation of the three-dimensional ultrasonic image recorded, two different three-dimensional views of the object examined are calculated starting out from a single data set stored in the memory unit and in each case assigned to one eye of the viewer, in order to make possible a three-dimensional visual perception of the ultrasonic image to this viewer.
However, the occurrence of artifacts, which cannot be differentiated in the recorded images from the real, reflecting structures of the object examined, is a disadvantage. In particular, when direction-dependent effects in the form of tail-like image patterns occur, there is a need to check the photograph for genuineness, since direction-dependent effects may be indications of pathological changes in the tissue investigated. Furthermore, the tail regions of the direction-dependent image patterns remain hidden to a viewer, since they lie, for example, behind strongly reflecting structures in the sound beam direction and do not generate any visible reflections.
In the DE 35 03 477 A1, an ultrasonic diagnosis device is disclosed, which comprises a rod-shaped linear scanner with piezoelectric elements disclosed next to one another. The linear scanner can be shifted in its transverse direction by a specified path length by means of a transporting unit. By means of the consecutive shifting of the linear scanner between scanning positions and the subsequent synchronized reading of its piezoelectric elements, sectional images in the longitudinal direction of the linear scanner, as well as sections at right angles to this of a breast, which is to be examined, can be represented on a screen unit. Here also, the frequently occurring artifacts make a medical evaluation of the ultrasonic images difficult. Furthermore, regions, lying behind strongly reflecting or reinforcing particles in the direction of the sound ray, remain hidden to the viewer.
In the DE 30 02 067 A1, an apparatus is disclosed, which permits an essentially fully automatic examination of a female breast. The apparatus comprises a couch with a resting surface, in which an opening has been provided. On the side of the couch, averted from the resting surface, a container is disposed, which is filled with water as coupling medium. Furthermore, a holding arm with at least one ultrasonic transducer is provided in the container. The holding arm is driven mechanically or electrically and carries out a semicircular swiveling motion, the center of which corresponds approximately to the center of the opening in the couch or is a few centimeters perpendicularly above the center of the plane of the opening in the interior of the thorax of the patient. During a swiveling motion of the holding arm carrying the or each ultrasonic transducer, a two-dimensional, level layer image is produced and stored in a memory unit. Furthermore, a transporting unit is provided for shifting the or each ultrasonic transducer, perpendicularly to the plane of swiveling of the holding arm or to the rotation of the swiveling plane about a common axis, by in each case a predetermined path length, so that series of level sectional images can be stored in a memory unit together with an assigned data value, corresponding to the respective shifting.
During the swiveling motion of the or each ultrasonic transducer about the breast, layer regions are scanned repeatedly, so that, because of the redundancies, averaging methods are required for representing the image. Admittedly, this method brings about a reduction in the interfering artifacts and permits all neighboring regions of strongly reflecting or reinforcing particles to be viewed. However, the occurrence of tail-like image patterns in two-dimensional sectional images, which is desirable with respect to a simplified diagnosis, is suppressed almost completely due to the averaging of the recording. Furthermore, the long measuring time of the apparatus disclosed here is a disadvantage, since the or each ultrasonic transducer, for recording a two-dimensional sectional image, already must be passed on a semicircular path about the breast, which is to be examined. Moreover, the movement of the holding arm causes a displacement, which in turn leads to a movement of the breast to be examined and, with that, to a deterioration in the quality of the layer image recorded.
From the DE 30 15 837 A1, an ultrasonic imaging apparatus with an ultrasonic transducer device is known, which has separate transducers for sending and receiving ultrasound. The height of the disclosed transducer device can be varied and the device is disposed in a water container and has a transporting unit for shifting the transducer laterally or on a circular path around the structure, which is to be examined.
From the journal xe2x80x9cFortschritte auf dem Gebiet der Rontgenstrahlung (Progress in the Field of X Radiation)xe2x80x9d, 147, 3 in the year 1987 in the article xe2x80x9cClinical Experience with Ultrasonic Reflection Computer Tomography of the Breastxe2x80x9d by M. Friedrich, F. Fobbe and A. Sparenberg on pages 298 to 303, a method is disclosed for which the patient, resting on a couch, immerses the breast, which is to be examined through an opening in the couch into a water bath. Furthermore, an ultrasonic transducer with four individual sound heads of different focal length is disposed in the waterbath. It is passed by a transporting unit by a predetermined path length on circular scanning paths about the breast protruding into the water bath. By shifting the ultrasonic transducer, any sectional images of the breast, which is to be investigated, can be produced. With the help of an averaging method, which is unavoidable with this scanning procedure because of redundancies, a reduction in image artifacts furthermore is made possible. Aside from the absence of tail-like image patterns due to the image averaging, the passing of the ultrasonic transducer on circular paths around the breast that is to be examined and the therewith associated long recording time, required for recording a two-dimensional sectional image, are disadvantages.
In the DE 80 10 553 U1, an ultrasonic diagnostic device is disclosed, which is provided particularly for examining the female breast and consists of a couch with a resting surface and an opening through the couch. At the side of the couch, averted from the resting surface, a container filled with water is disposed, so that the breast of the patient is immersed through the opening in the couch in the water, which has been filled into the container. Subsequently, a physician can commence to scan the breast, in that he passes conventional ultrasonic testing equipment manually along the outer wall of the container.
It is an object of the invention to provide an apparatus and a method of the type named above, which permits the genuineness of image structures, visible in ultrasonic images, to be checked particularly with respect to the direction-dependent effects, in order to increase the informative power of ultrasonic images for diagnostic purposes.
This objective is accomplished with the apparatus of the type named above owing to the fact that the or each ultrasonic transducer, for the purpose of obtaining level layer images extending at an angle to one another, is held by a tilting shaft which can be rotated by an adjustable tilting angle.
This objective is accomplished for the method of the type named above owing to the fact that the ultrasonic transducer is aligned by a rotatable tilting shaft at a tilting angle with respect to the at least one breast and stored with the assigned tilting angle and that at least two three-dimensional ultrasonic images are recorded and stored.
Scanning a breast with the assigned sound beam direction is made possible because the ultrasonic transducer is held by a tilting shaft. However, direction-dependent effects, such as shadows or reinforcing zones are retained by storing the image, which is not averaged and is recorded together with an assigned tilting angle and provide a viewer or an automatic evaluation method, which follows the measurement, with important information concerning pathological changes in the object being investigated. Moreover, artifacts and, in particular, artifacts of direction-dependent structures can be differentiated from real structures by comparing corresponding image regions of the stored data blocks. Moreover, with the help of the ultrasonic transducer, working in the so-called B mode and scanning a two-dimensional area, rapid recording and storage of three-dimensional data cubes is possible.
In the case of an advantageous embodiment of the inventive apparatus, the at least one breast can be passed through an opening in the couch, which is equipped with a resting surface. The or each ultrasonic transducer is disposed on the side of the couch, averted from the resting surface and a container, holding the coupling medium, is set up between the or each ultrasonic transducer and the at least one breast for holding the coupling medium.
In order to be able to adapt it individually to at least one breast, which is to be examined, the height of the container, holding the coupling medium, can be adjusted and the container is provided with elastic upholstery.
In an appropriate further development of the inventive apparatus, the or each ultrasonic transducer is disposed at the container holding the coupling medium and terminates flush with one side, facing the coupling medium, of a wall of the container holding the coupling medium, a volume displacement of the coupling medium as the ultrasonic transducer is shifted, being avoided.
In a preferred embodiment, an ultrasonic transducer is disposed in a sound head recess of a bottom wall of the container holding the coupling medium, which can be covered completely with coupling medium. To prevent the coupling medium running out, a flexible sealing unit is disposed at one side of the bottom wall, opposite the at least one breast. At one side of the bottom wall, facing the at least one breast, the sound head recess is bounded by a membrane permeable to ultrasound and at least one region of the bottom wall, encompassing the sound head recess, can be shifted.
In a further appropriate development, the transporting unit comprises two contacting rollers, which are disposed below the container holding the coupling medium and are set up for pressing the bottom wall against the sealing lips of the side walls of the container holding the coupling medium. The contacting rollers can be driven for rotating about a specified angle.
Advantageously, at least one ultrasonic transducer is disposed as a rodshaped linear scanner, on which a plurality of elements, generating ultrasound, are disposed next to one another. The linear scanner preferably is disposed essentially parallel to the resting surface and transversely to the longitudinal direction of the couch; it being possible to shift the whole of the bottom wall in the longitudinal direction of the couch.
In a preferred embodiment of the inventive apparatus, the linear scanner is configured so that ultrasound, sent out from it, scans two breasts when the bottom wall is shifted.
In an embodiment deviating from this, the linear scanner is equipped in such a manner, that ultrasound, sent out from it, scans one breast when the bottom wall is shifted, the linear scanner being mounted so that it can be shifted on a guiding rail transversely to the scanning direction for selecting the breast that is to be examined.
In a further development of the inventive apparatus, the linear scanner is disposed parallel to the resting surface of the couch and parallel to be the longitudinal direction of the couch, the whole of the bottom wall region being displaceable in the direction transverse to the couch.
In a further example at least one ultrasonic transducer is a sector scanner with a sector-shaped scanning region, which advantageously is displaceable with the bottom wall in the longitudinal direction of the couch, the scanning sector being aligned essentially transversely to the longitudinal direction of the couch.
At least one ultrasonic transducer of a further embodiment of the inventive apparatus is constructed as a sector scanner, which is mounted in the center of the bottom wall so that it can rotate about itself.
In an example deviating from this, at least one ultrasonic transducer is constructed as a linear scanner and disposed in a disk-shaped rotatable central region of the bottom wall, the central region being mounted rotatably by means of sealing units in the stationary region of the container holding the coupling medium.
In the case of an appropriate further development, at least one ultrasonic transducer is disposed in a side wall of the container holding the coupling medium, while in any case of an example, deviating from this, the bottom wall as well as the side wall each have an ultrasonic transducer.
Advantageously, in the case of the inventive method, the ultrasonic transducer is tilted differently for each of the three-dimensional ultrasonic images.
Advisably, the coordinates of ultrasonic image, recorded with a different tilting angle, are imaged by means of a mathematical conversion program on a common coordinate system.
In the case of an appropriate further development of the inventive method, the at least two ultrasonic images are compared by means of an evaluating program point by point by difference formation and any structures, occurring only in a single memory region, are discarded as artifacts.
Furthermore, it is appropriate to determine direction-dependent structures in the respective three-dimensional ultrasonic images by means of an evaluating program by scanning the image points in the vicinity of a fixed threshold value, to compare them with projection onto the respective scanning direction by subtraction and discard only structures, occurring in a single memory region, as artifacts.